Beverage dispensing systems such as the post-mix soda gun have been popular for at least twenty years and are now utilized in approximately 90% of the bars and cocktail lounges in this country. They consist of a dispenser handset with selection switches coupled with an under bar group of solenoid valves controlling pressurized syrup ingredients and carbonated water. Actuation of a selection switch opens a syrup valve and a carbonated water valve so the ingredients can flow to a mixing chamber in the handset through flexible delivery conduits before being dispensed.
Early liquor systems have utilized the same techniques with timer controlled solenoid valves regulating the flow of pressurized liquor. These systems were not successful sales wise, because the measured quantity was not consistant due to pressure variations, timer variations, and kinks in the delivery conduits. These slight variations are not readily noticeable when the end product such as cola is a mixture of ingredients, but when a one ounce shot of liquor is called for at over $100.00 a gallon, it must be exactly one ounce.
More recent liquor systems have utilized positive displacement pumps for exact measurement but they have suffered from the difficulty of changing the volume of the drink delivered. If the drink recipe called for a half measure or a half measure more there was no simple method of changing the volume delivered for that one drink or for a period of time such as a happy hour.
Previous attempts to control the volume dispensed include: U.S. Pat. No. 3,598,287 showing a knobwheel cooperating with a limit switch which must be adjusted manually. U.S. Pat. No. 3,830,405 shows an adjusting handle with threads to screw inwardly in order to limit the retracting movement of the piston. U.S. Pat. No. 3,785,526 shows a manually adjustable servo switch operated by a rack and pinion gear attached to the piston rod. The intent of the required manual adjustment was to insure the accuracy of each pump not to change the volume to be delivered by one pump for one dispensing cycle. It can also be appreciated that it would be impractical on a system involving 24 pumps to adjust all 24 pumps for the duration of a happy hour.
U.S. Pat. No. 3,830,405 shows a dispenser handset with both liquor and soda mix selection buttons but it is obvious that as the number of selections are increased the more confusing the selection becomes and the more chance there is for operator error.